Deployments

One thing you may be thinking you will be able to do with a ReplicaSet is rolling upgrades and rollbacks. Unfortunately, ReplicaSets can only replicate the same version of a pod; luckily, this is where deployments come in.

A deployment controller is designed to update a ReplicaSet or pod. Lets use NGINX as an example. As you can see from the following definition, we have 3 replicas all running NGINX version 1.9.14:

apiVersion: apps/v1beta1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  replicas: 3
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.9.14
        ports:
        - containerPort: 80

kubectl is the command-line client for Kubernetes; we will be looking at this in more detail in our next chapter.

We could deploy this using the following command:

$ kubectl create -f nginx-deployment.yaml

Now say we want to update the version of the NGINX image used. We simply need to run the following command:

$ kubectl set image deployment/nginx-deployment nginx=nginx:1.13.5 deployment "nginx-deployment" image updated

This will update each pod in turn until all of the pods are running the new version of NGINX.